#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	int n = 0;
	int i = 0;
    double sum = 0;
	int j = 1;
	int flag = 1;

	scanf("%d", &n);
	for (i = 1; i <= n; i++)
	{
		
		sum += (flag * (i * 1.0) / (j * 1.0));
		j = j + 2;
		flag = -flag;
	}

	printf("%.3lf", sum);

	return 0;
}